Interpretive Summary: Biological production of healthy fatty acids is of interest as a source of purer acids from traditional fish oil. Pythium irregulare is a type of fungus that can convert low concentrations of carbon into oil containing the fatty acid eicosapentaenoic acid. Submerged culture studies using this fungus were performed at three temperatures (14, 21, 28 degrees Celsius) to determine the temperature effects on the biomass and total oil production. Two growth parameters for the fungus were calculated from the logistic equation. These values were used to find the activation energy for the growth process. Fungal fermentations at 14 degrees Celsius gave the greatest biomass as well as the greatest oil concentration of eicosapentaenoic acid. However, growth at 21 degrees Celsius yielded the greatest ratio of lipid weight to biomass weight.

Technical Abstract:
Kinetic analysis was investigated for a carbon-limited medium, with a carbon-to-nitrogen ratio of 5.0, supporting the growth of the 5,8,11,14,17-eicosapentaenoic acid (20:5; omega-3)accumulating fungal organism Pythium irregulare. The productivity and yield parameters at three temperatures, 14, 21, and 28 degrees Celsius, demonstrated growth-coupled synthesis for lipid-free biomass growth and lipid accumulation. For this system, the maximum specific growth rate and theoretical maximum biomass yield based on logistic growth kinetics were used to determine an activation energy of the growth process, of 36.5 kilojoules per mol. At 14, 21, and 28 degrees Celsius, peak lipid yield occurred after culturing for 7, 4, and 3 days, respectively, with peak lipid yields of 8.14, 12.8, and 6.69 grams lipid per 100 grams of glucose. At these peak yields, the maximum lipid-free biomass productivity was achieved at the colder 14 degrees Celsius temperature as well as an increased concentration of eicosapentaenoic acid—10.9 wt%. Despite these enhancements, the maximum relative lipid production was achieved at 21 degrees Celsius—19.1%.